Stocking density and Piscirickettsia salmonis infection effect on Patagonian blennie (Eleginops maclovinus, Cuvier 1830) skeletal muscle intermediate metabolism

Immune Transcriptional Response in Head Kidney Primary Cell Cultures Isolated from the Three Most Important Species in Chilean Salmonids Aquaculture

Fish cell culture is a common in vitro tool for studies in different fields such as virology, toxicology, pathology and immunology of fish. Fish cell cultures are a promising help to study how to diagnose and control relevant viral and intracellular bacterial infections in aquaculture. They can also be used for developing vaccines and immunostimulants, especially with the ethical demand aiming to reduce and replace the number of fish used in research. This study aimed to isolate head kidney primary cell cultures from three Chilean salmonids: Salmo salar, Oncorhynchus kisutch, and Oncorhynchus mykiss, and characterize the response to bacterial and viral stimuli by evaluating various markers of the innate and adaptive immune response. Specifically, the primary cell cultures of the head kidney from the three salmonids studied were cultured and exposed to two substances that mimic molecular patterns of different pathogens, i.e., Lipopolysaccharide (LPS) (bacterial) and Polyinosinic: polycytidylic acid (POLY I:C). Subsequently, we determined the mRNA expression profiles of the TLR-1, TLR-8, IgM, TLR-5, and MHC II genes. Head kidney primary cell cultures from the three species grown in vitro responded differently to POLY I:C and LPS. This is the first study to demonstrate and characterize the expression of immune genes in head kidney primary cell culture isolated from three salmonid species. It also indicates their potential role in developing immune responses as defense response agents and targets of immunoregulatory factors.

Experimental transmission of Caligus rogercresseyi between two different fish species

Caligus rogercresseyi is the dominant sea louse parasite affecting the salmon and trout industry in southern Chile. This parasite has a wide range of native and endemic fish hosts. The Patagonian blenny Eleginops maclovinus, which is parasitized mostly by the caligid species Lepeophtheirus spp. and C. rogercresseyi, is presumably responsible for the transmission of C. rogercresseyi to salmonids. The aim of this study was to characterize the transmission of parasites between different fish species and parasite cohort development under laboratory conditions. Parasite abundances and intensities were quantified. Transmission of parasites from Patagonian blenny to Atlantic salmon Salmo salar was lower (~9%, mainly corresponding to C. rogercresseyi) than from salmon to Patagonian blenny (14.7-26.9%, where only C. rogercresseyi were observed). This suggests that the transmission of C. rogercresseyi from salmon individuals is higher than the transmission from a native fish. Parasite cohorts developed successfully on both fish species, but apparently under different developmental rates. Water temperature, oxygen, and juvenile abundances were the variables that better explained cohort development success and variation in C. rogercresseyi adult abundances over time.

Intermediary metabolic response and gene transcription modulation on the Sub-Antarctic notothenioid Eleginops maclovinus (Valenciennes, 1930) injected with two strains of Piscirickettsia salmonis

Pathogen interactions with cultured fish populations are well studied, but their effects on native fishes have not been characterized. In Chile, the disease caused by bacterial species Piscirickettsia salmonis represents one of the main issues and is considered to be one of the important pathogens in the field of aquaculture. They have been found to infect native fish. Therefore, it is necessary to understand the impact of P. salmonis on native species of local commercial value, as well as the potential impact associated with the emergence of antibiotic-resistant strains of P. salmonis. Due to this purpose, the native fish Eleginops maclovinus was used in our study. Fish were randomly distributed in tanks and intraperitoneally inoculated with two strains of P. salmonis. No mortality was recorded during the experiment. Cortisol, glucose and total α-amino acid levels increased in fish injected with AUSTRAL-005 strain compared to sham-injected and LF-89-inoculated fish. Moreover, results showed an increase in the activity of carbohydrates and lipids metabolism in liver; and an increase in the carbohydrates, lipids and total α-amino acid metabolism in muscle after injection with AUSTRAL-005. Our results suggest that P. salmonis modulates the physiology of E. maclovinus and the physiological impact increase in the presence of the antibiotic-resistant strain AUSTRAL-005.

Mechanosensory system of the lateral line in the subantarctic Patagonian blenny Eleginops maclovinus

This study describes the cephalic and trunk lateral line systems in Patagonian blenny Eleginops maclovinus juveniles, providing morphological details for pores, canals and neuromasts. Eleginops maclovinus juveniles possess a complete laterodorsal lateral line that extends from the upper apex of the gill opening along the trunk as far as the caudal fin. The lateral line was ramified through pores and canals. The following pores were recorded: four supraorbital pores, with two along the eye border and two on the snout; seven infraorbital pores, with three on the lacrimal bone and four being infraorbital; five postorbital pores, with three along the preopercular border (upper preoperculum branch) and two on the bone curvature (inferior preoperculum branch); and four mandibular pores aligned along the jaw. Furthermore, five narrow-simple and interconnected canals were found (i.e. preopercular, mandibular, supraorbital and infraorbital canals). Histologically, the dorsal lateral line presented thin neuromasts (350 μm) with short hair cells. By contrast, the cranial region presented long, thick neuromasts. Infraorbital and mandibular neuromasts had a major axis length of 260 μm and respective average diameters of 200 and 185 μm. Sensory system variations would be due to a greater concentration of neuromasts in the cranial region, allowing for a greater perception of changes in water pressure. Scarce morphological information is available for the lateral sensory system in Eleginopsidae, particularly compared to Channichthyidae, Bovichthydae, Artedidraconidae and Bathydraconidae. Therefore, the presented results form a fundamental foundation of knowledge for the lateral-line system in juvenile E. maclovinus and provide a basis for future related research in this taxon as well as within the Notothenioidei suborder.

Nutritional Immunity Triggers the Modulation of Iron Metabolism Genes in the Sub-Antarctic Notothenioid Eleginops maclovinus in Response to Piscirickettsia salmonis

Iron deprivation is a nutritional immunity mechanism through which fish can limit the amount of iron available to invading bacteria. The aim of this study was to evaluate the modulation of iron metabolism genes in the liver and brain of sub-Antarctic notothenioid Eleginops maclovinus challenged with Piscirickettsia salmonis. The specimens were inoculated with two P. salmonis strains: LF-89 (ATCC^® VR-1361™) and Austral-005 (antibiotic resistant). Hepatic and brain samples were collected at intervals over a period of 35 days. Gene expression (by RT-qPCR) of proteins involved in iron storage, transport, and binding were statistically modulated in infected fish when compared with control counterparts. Specifically, the expression profiles of the transferrin and hemopexin genes in the liver, as well as the expression profiles of ferritin-M, ferritin-L, and transferrin in the brain, were similar for both experimental groups. Nevertheless, the remaining genes such as ferritin-H, ceruloplasmin, hepcidin, and haptoglobin presented tissue-specific expression profiles that varied in relation to the injected bacterial strain and sampling time-point. These results suggest that nutritional immunity could be an important immune defense mechanism for E. maclovinus against P. salmonis injection. This study provides relevant information for understanding iron metabolism of a sub-Antarctic notothenioid fish.

Identification, characterization and modulation of ferritin-H in the sub-Antarctic Notothenioid Eleginops maclovinus challenged with Piscirickettsia salmonis

Ferritin is a major iron storage protein essential not only in the infectious process, but also in any circumstance generating oxidative stress. In this study, the cDNA coding sequence of ferritin-H was obtained from the sub-Antarctic Notothenioid fish Eleginops maclovinus through transcriptomic analysis of the head kidney. This sequence contained a 534 bp open reading frame that coded for a 177 amino acid protein with a molecular weight of 20,786.2 Da and a theoretical pI of 5.56. The protein displayed a region of iron putative response elements in the 5'UTR, two putative ferritin iron-binding region signatures, and seven characteristic amino acids with ferroxidase functions. Phylogenetic analysis related this sequence to ferritin-H sequences of other Antarctic Notothenioid fish, sharing 96.61% similarity. Constitutive gene expression analysis in different organs revealed increased ferritin-H gene expression in the gills, spleen, muscle, and liver. After infection with two bacterial strains of Piscirickettsia salmonis (LF-89 and Austral-005), ferritin-H was differentially expressed depending on bacterial strain and tissue. This study provides relevant information towards understanding the iron metabolism of a sub-Antarctic Notothenioid fish.

Stress response of Salmo salar (Linnaeus 1758) when heavily infested by Caligus rogercresseyi (Boxshall & Bravo 2000) copepodids

The year-round presence of ovigerous females of the parasite Caligus rogercresseyi in the fish farms of southern Chile results in a continuous source of the copepodid (infestive) stage of this louse. The short generation time in spring-summer could lead to high abundances of this copepodid, potentially leading to high infestation levels for fish. Knowing how heavy lice infestations affect Salmo salar can help determine how to time antiparasitic treatments so as to both minimize the treatment impact and reduce lice infestation levels for fish. This study aimed to describe the effects of high infestations of the copepodid stage of C. rogercresseyi on the physiology of S. salar. Two groups of S. salar were used: an infested group (75 copepodids per fish) and a control group (not infested). Sixty-five days after the first infestation, the infested fish group was re-infested at an infestation pressure of 200 copepodids per fish. Sampling was done prior to and following the second infestation, at 56 and 67 days (the latter 2 days following the second infestation). Several physiological variables were measured: cortisol (primary stress response) and glucose, proteins, amino acids, triglycerides, lactate, osmolality levels, and number and diameter of skin mucous cells (secondary stress responses). The plasma cortisol, glucose, and triglyceride levels were altered in the heavily infested fish, as was the diameter of skin mucous cells. These results suggest that heavy infestations of C. rogercresseyi lead to an acute stress response, metabolic reorganization, and increased mucus production in S. salar under heavy infestation conditions.

Effects on the metabolism, growth, digestive capacity and osmoregulation of juvenile of Sub-Antarctic Notothenioid fish Eleginops maclovinus acclimated at different salinities

In this study we assessed the influence of three different environmental salinities (5, 15 and 31 psu during 90 days) on growth, osmoregulation, energy metabolism and digestive capacity in juveniles of the Notothenioid fish Eleginops maclovinus. At the end of experimental time samples of plasma, liver, gill, intestine, kidney, skeletal muscle, stomach and pyloric caeca were obtained. Growth, weight gain, hepatosomatic index and specific growth rate increased at 15 and 31 psu and were lower at 5 psu salinity. Gill Na(+), K(+)-ATPase (NKA) activity presented a "U-shaped" relationship respect to salinity, with its minimum rates at 15 psu, while this activity correlated negatively with salinity at both anterior and posterior intestinal portions. No significant changes in NKA activity were observed in kidney or mid intestine. Large changes in plasma, metabolite levels and enzymatic activities related to energy metabolism in liver, gill, intestine, kidney and muscle were generally found in the groups exposed to 5 and 31 psu compared to the 15 psu group. Only the pepsin activity (digestive enzymes) assessed enhanced with environmental salinity, while pyloric caeca trypsin/chymotrypsin ratio decreased. This study suggests that juvenile of E. maclovinus presents greater growth near its iso-osmotic point (15 psu) and hyperosmotic environment (31 psu). Acclimation to low salinity increased the osmoregulatory expenditure as seen by the gill and anterior intestine results, while at high salinity, branchial osmoregulatory activity was also enhanced. This requires the mobilization of lipid stores and amino acids, thereby holding the growth of fish back. The subsequent reallocation of energy sources was not sufficient to maintain the growth rate of fish exposed to 5 psu. Thus, E. maclovinus juveniles present better growth efficiencies in salinities above the iso-osmotic point and hyperosmotic environment of this species, showing their best performance at 15 psu as seen by the main osmoregulatory and energy metabolism enzymatic activities.